app: verify unix socket path length in socket.tcp_server()

Providing socket pathname longer than UNIX_PATH_MAX to socket.tcp_server()
will not cause any error, lbox_socket_local_resolve will just truncate the
name according to the limit, causing bad behavior (tarantool will try to
access a socket, which doesn't exist). Thus, let's verify, that pathname
can fit into buffer.

Closes #4634